1. Field of the Invention
This invention relates generally to a fragmentation warhead of unique construction.
2. Description of Related Art
To avoid random distribution of fragments propelled by exploding anti-property and anti-personnel devices, it is necessary to control the size, shape, and weight of the fragments. Conventional warheads have included designs where separate munitions are positioned in a canister which, in turn, is contained within the missile structure. Preformed projectiles are positioned over the warhead and held in place by the exterior structure or shroud of the missile. However, in that prior scheme, the exterior structure of the missile tends to interfere with and disrupt the projectile pattern upon detonation of the missile, reducing the effectiveness of the missile warhead.
To address this problem, warheads have been designed in which the warhead casing becomes an integral part of the missile skin and structure. To accomplish this, accommodation of structural strength and fragmentation control must be provided. One prior approach to inducing fragmentation control to an integral warhead and missile structure has been to include grooves on either the external or internal wall surfaces of the structure to delineate fragments or projectiles in a combined warhead and missile structure. Explosives are installed in proximity to the grooves. When the explosives are detonated, the grooves create stress concentrations that cause the structure to fracture along the grooves, forming fragments. Generally, these grooves are longitudinal, circumferential, or both, designed to form rectangular fragments, or constitute a series of intersecting helical grooves designed to produced diamond shaped fragments.
For instance, U.S. Pat. No. 4,664,035 to Osofsky discloses a warhead in which the warhead projectiles are integrated into a missile structure. The integrated missile structure and warhead projectiles are fabricated by precision casting. The outer portion of the structure may be formed of a superalloy, such as nickel-based MAR-M200 (60% Ni), to resist heat. U.S. Pat. No. 4,503,776 to Nussbaum et al. discloses a fragmentation body for fragmentation projectiles and warheads in which prefabricated fragments are molded into a tubular fragmentation shell constituted of metal, or other suitable castable materials.
Despite these prior efforts, room for further improvement still has remained in the design of warhead structures desired to have both structural viability and fragmentation control upon detonation of the warhead, with the recognition that these dual objectives are often at odds with each other.
The above and other objects are achieved in accordance with the present invention directed to a fragmentation body for fragmentation projectiles and warheads, including an integral fragmentation shell structure having an outer wall surface and an inner wall surface separated by a thickness of the shell, where at least one of the inner or outer surfaces includes recesses formed through part of the thickness of the shell to define a plurality of fragments which remain integrated with the shell structure until an explosive force is detonated in proximity of the shell, wherein the shell material comprises a steel alloy including carbon, chromium, nickel, molybdenum, cobalt, and the balance essentially being iron. Shell structures of the inventive fragmentation body also have a fragmentation pattern defined via recesses or grooves provided in at least one of the inner or outer wall surfaces thereof to define the size and shapes of the fragment projectiles desired.
An important aspect of the invention is the use of an ultrahigh strength steel alloy of a specified composition as an integral controlled fragmentation body or warhead as well as to use it as a structural member of a missile. The steel alloy used in this regard is high strength, yet controllably fragmentable into desired and uniform individual projectile shapes and sizes, and in a desired overall dispersion pattern. A steel alloy found to meet both these criteria in the context of a recess-patterned fragmentation body comprises about 10-15 wt % nickel, about 0.75-1.75 wt % molybdenum, about 2-4 wt % chromium, about 0.2-0.35 wt % carbon, about 8-17 wt % cobalt, and the balance is essentially iron.
Shell structures of the inventive fragmentation body, as formed of the aforesaid steel alloy composition possess excellent mechanical properties, such as high tensile strength and fracture toughness, to permit lower overall weight amounts of the metal to be used in providing a structure which withstands the warhead acceleration loads and forces, while, at the same time, the metal structure nonetheless is amenable to groove/recess patterning therein yielding highly predictable and controllable fragment sizes and shapes, fragment velocity, and fragment distribution (dispersion) patterns, upon detonation of the warhead or missile incorporating same. Specifically, the aforesaid steel alloy composition permits provision of shear control grids in the shell structure, which cause the missile shroud to break into very small, uniformly sized fragments upon detonation of explosive charges carried by the warhead. The fact that the steel alloy used in the inventive fragmentation bodies is very high strength yet also very compliant to controlled fragmentation thereof is considered counter-intuitive and surprising to the present investigators.
Moreover, the aforesaid steel alloy composition is amenable to receiving a fragmentation pattern formed in the shell structure in situ by metal casting procedures. This cast construction averts the cost and timing otherwise associated with machining a fragmentation pattern into an initially continuous wall surface on a shell body. Also, the inventive fragmentation body conveniently can comprise energetic or reactive material positioned in the recesses defining the fragments. For purposes of this application, the terminology xe2x80x9cintegralxe2x80x9d, xe2x80x9cintegratedxe2x80x9d and the like, refer to a unitary, single-piece construction.